High efficiency switching amplifiers usable to amplify audio frequency signals are well known. One such amplifier system is disclosed in U.S. Pat. No. 3,185,768 to Cudahy entitled Amplifier Circuit.
Known switching amplifier systems generate a pulse width modulated switching signal in response to the applied audio input signal. The modulated signal includes components that replicate the audio input signal. In addition, it includes high frequency components associated with the frequency of the switching signal and its harmonics.
The modulated switching signal can be used to provide input signals to solid state switches. The solid state switches provide an output signal to a load.
Where the load has an inductive component, or there is an inductive filter in series with the load, the higher frequency components of the load current will be attenuated.
Because of limitations on the maximum value and the quality of the inductive components there can still be an appreciable current flow associated with the higher frequency components of the output signal. This current flow is especially apparent for small amplitudes of the audio input signal.
The use of an inductive filter is undesirable in that it increases amplifier size and weight. It also increases amplifier cost.
In addition, in the absence of a modulating audio input signal, the switching signal often appears at the load as a square wave. This square wave has an amplitude corresponding to the peak to peak output capability of the amplifier at the frequency of the switching waveform.
Such units tend to be used in a portable, battery powered environments. As a result, it is particularly desirable to minimize size and weight and losses of energy from the battery particularly when the input audio signal has substantially zero amplitude.